In recent years within the field of cardiology an increasing need for an effective, low complication prosthetic heart device has arisen. The natural heart may become incapable of maintaining adequate circulation because of various disease processes, including myocardial infarction.
Over the years, a number of artificial heart devices have been introduced in an attempt to restore normal function to otherwise failing hearts. The Jarvik-7 (J-7) artificial heart is one of the most famous and enduring of the prosthetic hearts. This device is an orthotopic design, which means it completely replaces the natural heart. It utilizes a semi-spherical ventricular chamber that contains a mobile internal diaphragm used for pumping blood. The J-7 heart is powered by an external pumping system and is used as a temporary life-sustaining measure in patients awaiting donor heart transplantation.
Multiple complications have become apparent after studying patients using the J-7 for prolonged periods of time. First, blood movement within the artificial ventricle is not uniform. Dead spaces and stagnant blood flow in peripheral areas of the semi-spherical chamber allow blood clots to form. Blood clots may then embolize into the general circulation and cause secondary complications including stroke. Second, structural compromise of the J-7 on adjacent thoracic structures including vasculature and pulmonary tissue may limit its application and create new problems in certain patients. Third, because this is an orthotopic design, the recipient's heart must be completely removed in order to attach the artificial heart. The decision to use a Jarvik-7 heart is therefore irreversible until a donor heart becomes available.
A second category of heart devices exist which work in conjunction with the natural heart in place. These pump devices secondarily augment the natural heart's function without requiring its removal and are referred to as orthotopic. In a recent study published in the New England Journal of Medicine, Feb. 11, 1988, Vol. 318, No. 6, pp. 333-340, a orthotopic system was utilized in which twenty-nine patients were followed over a three-year period. The results of the study showed that a orthotopic system could successfully maintain patients with irreversible heart failure in lieu of an orthotopic one.
A large advantage to a orthotopic system is that the option to pursue other possible medical or surgical interventions is preserved. The orthotopic system studied in the New England Journal of Medicine noted an extremely low complication rate associated with embolic events. The system, however, incorporates multiple externalized blood pumping tubes and used an external pump system. The National Institute of Health is currently funding research extending from the study previously cited in the New England Journal of Medicine. The orthotopic heart pump has been modified to remain within the confines of the human body. The pump, referred to as a left ventricular assist device (LVAD), channels blood entering the left ventricle to a pump located in the abdomen, then back into the abdominal aorta. Another pump system currently under investigation, which may be utilized under temporary circumstances, is the Nimbus pump system. The Nimbus pump forces blood flow by a set of rotating blades from the left ventricle into the aorta. Both pumps bypass blood flow around the weak left ventricle to augment circulation.
Therefore, a need exists for an effective orthotopic prosthetic heart device capable of augmenting right, left of both ventricles. It must not compromise thoracic structures or be prone to inducing blood clots or hemolysis. Blood flow characteristics should duplicate natural circulatory patterns and the pump should be responsive to normal increases or decreases in the body's physiological demands.
The heart device should minimize the risk of accidental blood loss by augmenting blood flow within the natural confines of the circulatory system, without externalized diversion. The system should be totally contained within the human body and be capable of sustained activity away from external power sources. Simple recharging methods should allow for quick, risk-free replenishment of the system's power supply. Such a system would not only serve as an effective temporary heart pump, but could also have significant potential for long-term use.